As your first question, higher species diversity might not lead to higher ecosystem productivity, but they provide more opportunities in maintaining ecosystem stability. That's the reason for more higher species diversity in tropical seas than bipolar seas.

The second question, in some extent, species diversity differ from ecological diversity. But it's hard to explain clearly.

Dr Chaofeng wang thank you for your contribution to the discussion

Increasing species diversity can influence ecosystem functions such as productivity by increasing the likelihood that species will use complementary resources and can also increase the likelihood that a particularly productive or efficient species is present in the community and positive relationship between diversity and productivity, while others have found no relationship or even a negative relationship. On the one hand, a diverse workforce can lead to increased creativity, innovation, and better decision-making, which can ultimately lead to increased productivity. In terrestrial ecosystems Tropical rain-forests show the highest productivity. In aquatic ecosystems, coral reefs have the highest productivity. Biodiversity insures ecosystems against declines in their functioning because many species provide greater guarantees that some will maintain functioning even if others fail. A diverse workplace adds new ideas and inputs. This diversity of talent means a broader range of skills among employees and a variety of experiences and perspectives, which increases the potential for increased productivity. Biodiversity boosts ecosystem productivity where each species, no matter how small, all have an important role to play. As larger number of plant species means a greater variety of crops. Greater species diversity ensures natural sustainability for all life forms. Species diversity represents the number and relative abundance of species in a biological community. Ecological diversity is the variety of ecosystems which indicates diversity in the number of niches, trophic levels, food webs, habitats, preferences and activity of species of a similar group. Biodiversity is a complex term that includes not only the variety of different animals but also the difference between animals of the same species and between ecosystems. The variation in productivity increases with species richness at any time and the selection process through dominance picks up the most productive species within this variation; as a result, productivity increases with species richness.